Can the regulatory issues be overcome?

‍‍Federal regulations that prohibit civilian supersonic flight over land in the United States‍:‍

14 C.F.R 91.817 and its accompanying Appendix B to 14 C.F.R Part 91 (2012) state, in part, that flight of a civilian aircraft above Mach 1 is permitted only if “(T)he flight will not cause a measurable sonic boom overpressure to reach the surface;"

No specifications or limitations on acceptable levels of overpressure are specified but some manufacturers are focusing on the 70 perceived loudness in decibels (PLdb) range as their targets, per NASA research targets (Garvey, 2010);

Most designers and manufacturers are proceeding with their work with the assumption that once technology can prove acceptable levels could be attained, the FAA will change its regulations (Aronstein & Schueler, 2005);

As late as 2008, the FAA maintained that supersonic aircraft can have no greater noise or sonic boom impact than subsonic aircraft although the agency concedes that “Noise standards for supersonic operation will be developed as the unique operational flight characteristics of supersonic designs become known and the noise impacts of supersonic flight are shown to be acceptable” (Federal Aviation Administration, 2008, p. 3).

Does/will the technology exist?

Sonic Boom mitigation is the most important issue to conquer:

Sonic booms are created by the shock waves produced at altitude by an aircraft traveling at supersonic speeds.

These waves then propagate to the ground, creating a change in pressure and generating a considerable disturbance (Candel, 2004);

A graph of the pressure wave over time resembles the letter “N” with a nearly instantaneous initial shock, spiking pressure upward above ambient pressure, followed by a nearly linear decrease to less than ambient pressure over the next several milliseconds, followed by a tail shock that recovers to ambient pressure (Aronstein & Schueler, 2005);

The noise level generated by the Concorde’s boom was 105 PLdb, louder than a jack hammer (Warwick, 2011b). Industry is aiming for a reduction to about 70 PLdb which is closer to a conversational noise level (Warwick, 2011b);

The most prevalent design theory to mitigate sonic booms was originated in a series of papers in the 1960’s and 1970’s and focuses on shaping the aircraft to correspondingly shape the shock wave, reducing the upward spike and the lower spike (Morgenstern, Arslan, Lyman, & Vadyak, 2005):

In 2003, the theory was conclusively proven through a series of tests funded by the Defense Advanced Research Projects Agency which used two F-5 aircraft, one left in production configuration and the other specially designed to soften the N-wave and reduce the impact at ground level (Morgenstern et al., 2005);

The tests showed that the shaped aircraft produced a consistent and significant reduction in the propagation of overpressure and sound to ground level, even in a turbulent atmosphere (Morgenstern et al., 2005). Gulfstream and other aircraft manufacturers performed wind tunnel tests that also confirm that shaped aircraft designs can reduce the sonic boom to acceptable levels (Henne, 2005);

Researchers at NASA have produced feasible designs which reduce the sonic boom to the range of 65-75 PLdb (Welge, Nelson, & Bonet, 2010);

NASA’s N+3 studies have indicated a low boom supersonic business jet could be technologically viable as early as 2015 (Warwick, 2010);

In May of 2012, researchers from Japan further confirmed the theory when they dropped two asymmetric aerodynamic bodies from high-altitude over Sweden and noted that the specially shaped body reduced the sonic boom by 50% (Warwick, 2011b).

Which designs show the most promise?

Aerion SSBJ

Aerion uses Mach Cutoff to avoid FAA regulatory issues for over land flight:

Boomless flight is not restricted to subsonic speeds;

Because of the temperature and sound speed gradients in the atmosphere, there is a cutoff Mach number below which the boom from a supersonic aircraft will not propagate to the ground;

For stratospheric flight in the U.S. Standard Atmosphere, the cutoff Mach number is 1.15. This represents a speed 35% faster than typical subsonic civil cruise speeds of Mach 0.85 or less (Plotkin, Matisheck, & Tracy, 2008);

Using a cutoff altitude of 5,000 feet for the sonic boom and depending on atmospheric conditions, Aerion’s jet could cruise at an indicated Mach number between 1.03 and 1.3 at an altitude between 45,000 and 50,000 feet and realize an average ground speed of 764 mph for eastbound trips and 754 mph for westbound trips (Plotkin et al., 2008);

These speeds are 29% and 47% higher than the average speeds for subsonic aircraft cruising at Mach .85 of 594 mph and 512 mph for eastbound and westbound trips respectively (Plotkin et al., 2008);

Most airliners and business jets cruise at Mach .80, making the speed advantage for the Aerion jet even greater.

An additional interesting feature of the Aerion jet is its use of natural laminar flow as a drag reduction mechanism at high speed which allows the use of a wing design that is not swept nearly as severely as that of most supersonic designs (Sturdza, 2007);

A wing that is more conventionally shaped allows for better slow-speed handling characteristics in the take-off and landing phases of flight without the use of sophisticated, heavy and cumbersome variable geometry designs (Sturdza, 2007);

Aerion’s choice of engine is an adaptation of the venerable and proven Pratt and Whitney JT8D-200 engine which currently powers the McDonnell-Douglas MD-80, Boeing 737-200 and Boeing 727 (Aerion Corporation, 2012; Pratt And Whitney Corporation, 2012).

Hypermach Aerospace Ltd.’s SonicStar, a jet that will enable boomless flight over land at speeds approaching Mach 4 through the use of cutting-edge technology that eliminates the sonic boom (Hypermach Aerospace Ltd., 2011a).

Rather than relying solely on aerodynamic design, the SonicStar relies on a unique solution, injecting plasma to rapidly heat an extended path ahead of the shock wave and thus creating a hot, low-density core through the rapid expansion of the plasma (Hypermach Aerospace Ltd., 2011b).

According to Hypermach’s description, the “vehicle’s bow shock expands into the core, followed by the vehicle itself. The shock bows as the core provides a route for the high pressure front to escape around the vehicle, reducing the shock strength” (Hypermach Aerospace Ltd., 2011b).

The creation of the quantity of plasma energy necessary to produce this effect is made possible by the SonicStar’s engine, originally called S-MAGJET (“S” for supersonic), a five-stage electric-turbine hybrid engine, now being developed into a hypersonic derivative called H-MAGJET (“H” for hypersonic) by Portland, Maine-based SonicBlue (Trauvetter, 2011).

The S-MAGJET engine design uses a superconducting ring motor-driven fan, compressor and turbines, and a combustion chamber that converts air into plasma via the following process:

As air enters the engine, it is accelerated in the first stage of a dual counterrotating bypass fan section, where it enters an eight-stage counter-rotating, statorless compressor. The compressed air reaches about 2,250F, and then is forced into an ion plasma fuel combustor and ignited by an array of electric- and magnetic-field-generating fuel injectors. The air is converted into plasma within the combustor before exiting to drive a five-stage counter-rotating gas turbine and integrated superconducting electric generator (Wall & Norris, 2011);

The fan assembly which produces the engine’s thrust is driven by turbines that are magnetically levitated and not mechanically connected to the core, hence fan RPM is completely independent of core RPM and the fan assembly can make use of larger, more aerodynamically efficient blades, improving the engine’s efficiency (HyperMach Aerospace Ltd, 2011c; Wall & Norris, 2011);

The S-MAGJET design boasts a specific fuel consumption (SFC) ratio (pounds of fuel burned / pounds of thrust) of 1.05 – 1.10 (Trauvetter, 2011). While this SFC is roughly twice that of typically modern airliners, it is well less than the Concorde’s SFC of approximately 1.2 and renders about twice the speed in return (Steelant, 2006);

SonicBlue’s engine technology was developed in 2006 by Richard Lugg, the current CEO of Hypermach, has been granted several US patents and has been pronounced viable by at least one industry expert, Sam Wilson, the president of AVID LLC, a Virginia fan-design company that has done work for a number of aerospace companies (Wickenheiser, 2006).

Does/will the demand exist for time savings?

Yes – business jet use is tied to the value of time

Example:

Assume that a corporation requires five executives to travel from New York to Los Angeles and these executives earn a combined total of $8,000,000[1] annually, based on a 40-hour work week and four weeks of yearly vacation, that means these executives’ time, collectively, is valued at $4,167 per hour.

The average block time for the airline flight is 6 hours 20 minutes and if we add an hour thirty minutes prior to the flight for check-in and security screening and another half hour at the destination to depart the aircraft and claim luggage, that makes the total journey time 8 hours and twenty minutes.

The total trip costs appear in Table SSBJ-1 below and make the case that when opportunity cost is taken into account, the value of time can make travel by business jet the right economic decision.

As far as the larger industry picture is concerned, market analyst Forecast International’s study estimates industry output at 683 jets for 2011, 728 jets in 2012 and while most manufacturers won’t reach their 2008 peak of 1,313 jets until 2018, the study predicts a total of 10,907 new business jets will be delivered between 2011 and 2020 with an estimated value of more than $230 billion (Epstein, 2011).

Outlook for faster, longer range and more expensive jets continues to improve and reflects a demand that could be filled by jets that are capable of vastly increased speed.

Even as economic conditions deteriorated in 2008, Gulfstream announced it would be building the fastest and longest range business jet in the world, the G-650, with a top speed of Mach .925 and a range of 7,000 nautical miles at Mach 85 and 5,000 miles at Mach .92 (Warwick, 2011a).

As of early 2012, Gulfstream has 200 orders for the G-650, a jet that is priced at $64.5 million (Trautvetter, 2012; Huber, 2011).

Bombardier plans to counter with its Global Express 7000 and 8000 models in 2016 and 2017 respectively (Warwick, 2011a).

Both jets will feature maximum ranges over 7,000 nautical miles at Mach .85 and high-speed cruise ranges over 5,000 nautical miles at Mach .90 and both will cost at least $5 million more than the G-650 (Warwick, 2011a).

If companies like Gulfstream and Bombardier continue to invest in production of ever-faster, ever-longer ranged aircraft with ever increasing price tags even in periods of recession, the economic justification for the SSBJ, like the technical accomplishments required, seems to just be a matter of time.

Henne (2005) agrees, arguing that the ever-increasing value of time is what has led to interest in the SSBJ in the first place and concluding that the “step to supersonic speeds offers the potential of a dramatic decrease in travel time” (p. 765).

Time savings for Aerion SSBJ using same five executives from first example, shown in Table SSBJ-2

Aerion maintains that the operating costs of their aircraft, on a cost per nautical mile basis, will be comparable to those of business jets like the G-450 and G-550 (Moll, 2010).

On a westbound trip using from JFK to LAX using Mach Cutoff, Aerion believes their jet will realize approximately a 45% time savings over a subsonic business jet cruising over the same route at Mach. 85 (Plotkin et al., 2008).

Table SSBJ-2

Real Trip Costs Expressed as a Value of Time – Aerion SSBJ, G-550 and Airliner

The Value of time is even more pronounced for Hypermach SonicStar given its advertised ability to fly from New York to Dubai in two hours and twenty minutes (Trauvetter, 2011).

With estimated operating costs that are twice as high as the G-550 (and the G-650’s costs will be comparable), the SonicStar’s much greater speed makes it less expensive to operate. This comparison is shown in Table SSBJ-3.

Table SSBJ-3

Real Trip Costs Expressed as a Value of Time – SonicStar, G-550 and Airliner